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Volcanic Hazards
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting Eruptions
Monitoring the Movement of Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Physical Anomalies and Precursor Phenomena
-ground deformation
-change in heat output
-change in the composition of gases
-local seismic activity
Basaltic eruptions are very fluid and will flow great distances from the vent or
rift. The photo above is taken from the Kilauea rift zone on the Big Island of
Hawaii.
Aa Flow, Hawaii
Pahoehoe Flow, Hawaii
Few fatalities are typically associated with basaltic lava eruptions, as
neighborhoods, such as the one shown here, can be evacuated. Buildings and
other human-made structures are not so lucky!
Basaltic lava flow reaching a neighborhood near
Kilauea, Hawaii.
Lava flow induced fire, Hawaii.
Pyroclastic eruptions and flows produce some of most devastating effects
associated with volcanism. Destruction is total to any living organism or structure
within the pathway of a pyroclastic flow.
Landslide north face of Mt. St. Helens May 18, 1980.
Mt. St. Helens May 18, 1980
Mount St. Helens: Pyroclastic flow May 18, 1980.
Bishop ash was erupted catastrophically 760,000 years ago in eastern California.
The eruption had a VEI = 7 and ashfall accumulated as far Nebraska.
Pompeii, Italy 79AD
Volcanic Hazards
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting Eruptions
Monitoring the Movement of Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Physical Anomalies and Precursor Phenomena
-ground deformation
-change in heat output
-change in the composition of gases
-local seismic activity
Causal Factors for Lahar
Flows
Lahar flow from
Mt. Pinotubo.
Volcanic tephras are well-preserved
in lacustrine and bog sediment
throughout the Cascades.
Ubiquitous organic matter provides
excellent opportunities to assign
radiocarbon ages to the eruptions.
The Mt. Mazam O (Crater Lake)
eruption occurred ~6800 years ago.
Excavating a trench behind the Hyak moraine at Snoqualmie Pass (ca. 1990).
Mt. St. Helens Wn
Mt. St. Helens Yn
Mazama O
Three tephra layers are presnt in the sediment record at Snoqualmie Pass. They
have been independently dated using radiocarbon dating of associated organics.
Tephra distribution from Mt. Mazama,
Longvalley and Yellowstone eruptions.
Tephra distribution of Cascade volcanoes
Isopachs of Glacier Peak tephra distribution (13,100 yr BP).
Isopachs of Glacier Peak tephra distribution (13,100 yr BP).
Mt. Rainier’s elevation exceeded
16,000 feet above sea level 5000 years
ago.
Following a large edifice collapse
~5000 years ago the mountain
lost ~1500 feet of its summit.
Mt. Rainier contain 90% of the
Cascade’s glacial ice and
permanent snow.
Mt. Rainier’s glacial ice is a major
potential source
Oceola Lahar (~5200 yr BP) near Enumclaw,
WA.
Glacier Peak has been active Cascade volcano over the past 15,000 years.
Unconsolidated pyroclastic deposits on north face of
Mt. St. Helens source of lahar flows.
Reworked pyroclastics incorporated into Mt. St.
Helens lahar deposits.
Volcanic Hazards
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting Eruptions
Monitoring the Movement of Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Physical Anomalies and Precursor Phenomena
-ground deformation
-change in heat output
-change in the composition of gases
-local seismic activity
Can we predict volcanic eruptions?
Yes, but with caveats!!!
1.Requires a thorough understanding of the volcano’s
eruptive history.
2.Requires appropriate instrumentation on the volcano
well in advance of the eruption.
3.Requires constant monitoring of instrumentation so that
incoming data can be properly interpreted.
The science behind predicting volcanoes has improved
substantially over the past decades, but volcanologists
can only provide probabilities regarding the timing of a
given eruption. It is not possible to determine the exact
severity of an eruption or whether the magma will even
reach the surface.
How do volcanoloists
predict volcanic
eruptions?
1.Monitor seismic data
related to movement of
magma.
2.Monitor ground
deformation and dome
expansion.
3.Monitor volcanic gases
emitted as magma rises
and expanding gases are
released.
Successful Volcanic Predictions:
Volcanologists predicted the eminencne 1980 Mt.
St. Helens eruption. Their warnings of an
impending blow prompted the U.S. Forest Service
to evacuate people from dangerous areas near the
volcano. Although 57 people died in the eruption, it
is estimated that as many as 20,000 lives were
saved.
In the spring of 1991, a USGS “SWAT team” was rushed
to the Philippines' Mt. Pinatubo and successfully
predicted the June eruption, leading to evacuations that
saved thousands if not tens of thousands of lives and
millions of dollars worth of military equipment at the
nearby Clark Air Force Base.